Cooling and crystallization in sheet-like magma bodies revisited

In order to characterize the interaction of convection and crystallization during the solidification of magmatic sills, a one-dimensional model for the solidification of magmatic sills cooling from above has been used. The model is based on a Stefan-type solution for a mushy zone and takes into account the inward moving solidification front, whose speed is exclusively controlled by crystal growth. Below the solidification front, the magma cools by convection. It may eventually cool below its liquidus and start to partially crystallize. A kinetic model has been implemented to account for this crystallization. The model calculations lead to three main conclusions: (1) Crystal growth is not the only factor controlling the advance of magmatic solidification fronts. The advance appears to be mainly controlled by nucleation processes and only to a small extent by crystal growth. (2) The longevity and vigor of convection inside a magma chamber is strongly dependent on the kinetics of crystallization of magma inside the chamber. (3) Immediately after the initiation of cooling the melt becomes laced with nuclei.